1. Field of the Invention
The invention is generally related to controlling power distribution from a single power source to multiple components. More particularly, this invention is related to distribution of RF power to a plurality of radio frequency (RF) coils disposed on a RF plasma reactor.
2. Background of the Related Art
Plasma reactors are typically employed in performing various processes on semiconductor wafers, including etching processes and chemical vapor deposition processes. An inductively coupled RF plasma reactor typically has an inductive coil antenna wound around the reactor chamber and connected to a plasma source RF power supply. An inductively coupled RF plasma reactor can achieve a very high plasma ion density for high production throughput, while avoiding a concomitant increase in ion bombardment damage of the wafer.
Inductively coupled plasma reactors typically have a plasma ion density distribution that can vary greatly depending upon various processing parameters, including the particular process gas or gas mixture introduced into the reactor chamber. For example, the plasma ion density may be high at the wafer center and low at the wafer periphery for one process gas, while for another process gas it may be the opposite pattern (i.e., low at the wafer center and high at the wafer periphery). As a result, the RF coil designs are customized for each different process or process gas to provide commercially acceptable uniformity across a wafer surface in the reactor. A plurality of RF coils, typically two coils, are utilized to improve plasma uniformity in the processing chamber, and each RF coil is connected to a separate individual RF power source through separate RF match networks dedicated to control the amount of RF power delivered to the RF coil.
FIG. 1 is a cross sectional schematic view of a typical plasma processing chamber having two RF coils disposed on a lid of the chamber. The plasma processing chamber generally includes a vacuum chamber 10 having a generally cylindrical side wall 15 and a dome shaped ceiling 20. A gas inlet tube 25 supplies process gas (e.g., chlorine for etch processing) into the chamber 10. A substrate support member or wafer pedestal 30 supports a substrate, such as semiconductor wafer 35, inside the chamber 10. An RF power supply 40 is also typically connected to the pedestal 30 through a conventional RF impedance match network 45. A plasma is ignited and maintained within the chamber 10 by RF power inductively coupled from a coil antenna 50 consisting of a pair of independent (electrically separate) antenna loops or RF coils 52, 54 wound around different portions of the dome-shaped ceiling. In the embodiment shown in FIG. 1, both loops are wound around a common axis of symmetry coincident with the axis of symmetry of the dome-shaped ceiling 20 and the axis of symmetry of the wafer pedestal 30 and wafer 35. The first RF coil 52 is wound around a bottom portion of the dome-shaped ceiling 20 while the second RF coil 54 is positioned centrally over the ceiling 20. First and second RF coils 52, 54 are separately connected to respective first and second RF power sources 60, 65 through first and second RF impedance match networks 70, 75. RF power in each RF coil 52, 54 is separately controlled. The RF power signal applied to the first RF coil (bottom/outer antenna loop) 52 predominantly affects plasma ion density near the periphery of the wafer 35 while the RF power signal applied to the second RF coil (top/inner antenna loop) 54 predominantly affects plasma ion density near the center of the wafer 35. The RF power signals delivered to each of the RF coils are adjusted relative to each other to achieve substantial uniformity of plasma ion distribution over a substrate disposed on a substrate support member.
The addition of an independent RF power source and associated RF impedance match network for with each RF coil increases the equipment and operation costs for each additional RF coil utilized on a processing chamber, resulting in increased cost for processing wafers. Furthermore, the independent RF source and matching network configuration presents difficulties in matching the impedance of the coils, which leads to more difficulties in controlling the plasma power delivered to each of the coils.
Another attempt to control plasma power in an inductively coupled plasma reactor having multiple coils utilizes a plurality of high power relays for switching connection from the power source to each of the coils. However, the switching mechanisms do not provide efficient operation of the coils and do not provide sufficient control of the power delivered to each of the coils on a continual basis.
Therefore, there is a need for an apparatus for distributing power from a single power source to a plurality of coils disposed on a processing chamber which provides controllable plasma uniformity across a substrate disposed in the processing chamber.
The invention generally provides method and apparatus for distributing power from a single power source to a plurality of coils disposed on a processing chamber which provides controllable plasma uniformity across a substrate disposed in the processing chamber.
The apparatus for distributing power from a power source to two or more coils disposed on a process chamber comprises a connection between the power source and a first coil; a series capacitor connected between the power source and a second coil; and a shunt capacitor connected to a node between the second coil and the power source, the shunt capacitor being connectable to a ground connection.
The method for distributing power from one power source to a plurality of coils comprises connecting a first coil between the power source and a ground connection; connecting a power distribution network to the power source, wherein the power distribution network comprises a series capacitor and a shunt capacitor; and connecting a second coil between the power distribution network and a ground connection.
The invention also provides an apparatus for plasma processing comprising a chamber; a first coil and a second coil disposed on the chamber; a power source connected to the first coil; and a power distribution network connected between the second coil and the power source, the power distribution network comprising a series capacitor connected between the power source and the second coil; and a shunt capacitor connected to a node between the second coil and the power source, the shunt capacitor being connectable to a ground connection.